The invention relates to a method and apparatus for the use of radiation sources in therapy, and in particular to a miniaturized radiation source having the capability of being switched on and off at the operator's discretion. 2. Related Art
The manufacture of radiation devices has been developing during the last 30 years. The primary applications for these devices are in microelectronics, diods and transistors. However more recently, devices that generate radiation in the visible frequency region have been used for displays of the Flat Panel Display type, and this technology has become a separate research area for applications in the television field, etc. The primary effort has been to decrease the anode to cathode voltage, so that these devices can be used in general purpose electronic circuits. A more detailed description of this research can be found in an article entitled "Vacuum Microelectronic Devices", in Proceedings of the IEEE, Vol. 82 no. 7, July 1994.
In this article there are disclosed the principles and basic construction of micro field-emission sources. It is stated therein that it is necessary to have emission areas no larger than 10.sup.-2 cm.sup.2 in order to obtain uniform field emission. Therefore, it is necessary to form the emitter in the shape of a needle with a tip having an end radius less than 1 .mu.m. A specific design of the emitter is a metal cone, 10.sup.-4 cm tall with a tip radius of 30 nm. Also, there is disclosed the provision of an accelerating electrode (gate) spaced 60 from the tip.
In this application, these field emitting devices, among others, can be utilized to emit ionizing radiation with energies high enough to be used for medical therapy.
Radiation therapy is a well established method for treatment of several serious diseases, including cancer. Either alone or combined with other forms of therapy, the irradiation of human or animal tissue with ionizing radiation has proven to be very effective, and is used throughout the world and at several levels in health care organizations from specialized university clinics to regional and county levels. However, complications and side effects are often present. Ionizing radiation is biologically destructive in the sense that the structure of biomolecules is irreversibly changed, frequently leading to cellular disorganization, functional damage and even death. The result is also non-specific. A common problem is to limit the radiation exposure to areas of disease, to avoid destruction of healthy tissue.
Traditional radiation therapy makes use of radioactive nuclei, particle accelerators or high voltage generators to create radiation with such a high energy that it penetrates the patient's body. The radiation source is usually located outside the body, and means for collimating the radiation is used to concentrate it on the tissue where therapy is required. A difficult compromise is to maximize the therapeutic dose while minimizing the radiation exposure to healthy tissue.
In recent years, miniaturized radiation sources consisting of radioactive substances contained at the tip of a metal wire have been introduced. With such a localized radiation source it is possible to concentrate the dose to a small region. However, the use of radioactive substances is impractical for several reasons. First, the source must be properly shielded during introduction into the body to avoid exposure to healthy tissue. Second, all handling procedure must be carefully controlled to avoid exposure by mistake. Third, the dose and energy of radiation are not easily controlled.